This invention relates to an engine control installation and more particularly concerns an installation for starting and operating an engine intended for submarine operation or otherwise operating in an environment which lacks air.
A need exists to develop internal combustion engines for submarines which are capable of covering the field of application existing between accumulator operation and atomic operation. This need has been felt for a long time and has even greater significance today due to the applications in the field of research and exploitation of the seabed with the aid of submarines of small displacement and medium power but of the longest possible range.
The results of the studies and trials hitherto performed with a view to the development of an engine which could fulfill this need have not yet led to the realization of a satisfactory serviceable unit.
The basic idea pursued by all researchers was to use a conventional internal combustion engine and to convert the latter, after it had been started, into an internal combustion engine with exhaust gas feedback for submarine operation. This basic idea imposed a serious compromise because the internal combustion engine must be operated in continuous service with a medium, the physical and thermodynamic characteristics of which differ greatly from the characteristics underlying the design of the internal combustion engine. The necessity of starting the engine with air also makes it necessary to carry an appropriate quantity of air for possible underwater starting.
To particularize, the following disadvantages have appeared in these experiments and have certainly negated the possibility of realizing a technically satisfactory engine for submarine operation hitherto:
The unavoidable reduction in the thermodynamic efficiencies and hence the increased consumption of fuel and combustion support; here the increased consumption of combustion support obviously represents the most highly critical condition for the submarine unit. PA0 The necessity to preheat the intake mixture so that adequate temperature values can be attained after compression; the preheating of the gas mixture, as it has been performed in isolated cases by mixing the gases fed back after the scavenging with a part of the exhaust gases, also involves contamination problems in the internal combustion engine. PA0 The necessity to carry on board an appropriate supply of compressed air for possible underwater starting. PA0 Choice of the gas mixture and of the type of fuel with a view to optimum conditions for efficiency and consumption, also practical possibilities for a simple and economical reproduction of the optimum intake mixture during continuous operation. PA0 The problems related to accident safety also had to be taken into consideration, particularly since--since it is a question of dosing the gas mixture with pure oxygen--the possibilities of the use of gas mixtures enriched with oxygen may be considered with a view to improving efficiency. PA0 Use of such measuring, control and supply devices for fuel and oxygen as permit the optimum conditions for the combustion process and the stability of the internal combustion engine. PA0 Choice of the mechanical characteristics of the internal combustion engine which lead to optimum performance with the chosen gas mixture. The study of this problem revealed that an internal combustion engine for exclusive submarine operation, in which the efficiency values are required to be optimized, must be designed almost entirely "ad hoc". The most important differences compared to an engine for submarine operation which has been designed according to the previous principles of other researchers, are to be seen principally in the compresion ratio, the geometry of the combustion chamber, the stroke ratio, the preinjection and the injection time. PA0 Use of devices which permit such a separation of the carbon dioxide produced as a combustion product from the exhaust gas, so that the carbon dioxide can be removed and the oxygen still present in the exhaust gas can be recovered in a more or less complete manner. PA0 Use of devices for a simple and economic removal of the combustion products (essentially carbon dioxide and steam) from the circuit of the internal combustion engine, more particularly with the property of not being constrained to the immersion depth of the installation. PA0 .gamma.=ratio c.sub.p /c.sub.v of the specific heat at constant pressure to the specific heat at constant volume of the gas mixture, PA0 R=characteristic constant of the gas mixture, PA0 T=absolute temperature of the gas mixture.
An object of the present invention is to obviate these and other disadvantages. The invention is based upon an underlying idea which is totally different from the prior art, that the internal combustion engine should, from the starting process, embrace those peculiar operating conditions which are determined by submarine operation. In this way it becomes possible to develop an internal combustion engine which is capable of providing optimum performance even in an environment of other than air, so that one escapes the compromise which was imposed by the conventional double use, namely, starting with air and continuous operation with a medium other than air.
According to the present invention I provide an installation for starting and operating an engine intended for operation in an environment lacking air, characterized by an internal combustion engine so designed that it is operated with a gas mixture of previously prepared composition both during starting, and in continuous operation, while the previously prepared composition is chosen with a view to the optimum operating capacity which can be attained by the internal combustion engine.
An internal combustion engine based on the diesel principle has been taken as a basis for study. The unit has successfully passed the capability tests and can be considered as a serviceable unit.
The following principles were taken into consideration in the application of the idea of the invention with a view to achieving optimum results:
The gas mixture of previously prepared composition conveniently consists essentially of combustion gases, a fuel gas (e.g., O.sub.2) and optionally further inert gases.
In a preferred embodiment the installation according to the invention incorporates at least one tank in which the gas mixture of a previously prepared composition is contained.
In a preferred embodiment the installation includes a device for monitoring and regulating the oxygen supply necessary for submarine operation, which comprises means for measuring the instantaneous oil delivery rate, means for measuring the instantaneous percentage oxygen content in the intake mixture of the internal combustion engine, while said percentage oxygen content can be deduced from the function "sound transmission velocity in gas mixture-temperature", and an electronic calculator which serves to evaluate the two measured values detected with the aid of the above means, to compare them with prescribed optimum values for the operation of the internal combustion engine and, as dictated by that comparison, to control an oxygen dosing device for the oxygen supply to the intake mixture.
The said means of measuring the instantaneous percentage oxygen content in the intake mixture of the internal combustion engine are based upon the knowledge that the sound transmission velocity in a continuous gaseous medium is a function of the characteristics of the gas and of the temperature in accordance with the known relation: ##EQU1## wherein V=sound transmission velocity in the gas mixture,
The measurement of the temperature of the gas mixture (carbon dioxide, oxygen and steam) makes it possible to reduce the number of unknowns in the composition of the gas mixture from 3 (CO.sub.2, O.sub.2, H.sub.2 O) to 2 (CO.sub.2, O.sub.2). It is therefore possible to deduce from the measurement of the sound trasmission velocity at a given temperature, the value of the parameter .gamma.R which is a function of the percentage content of the constituents CO.sub.2 and O.sub.2 which constitute the gas mixture.
The dosing device for the oxygen supply to the intake mixture is conveniently controlled by electric valves which control a continuous oxygen current of variable quantity which is produced as the sum of discrete partial oxygen currents.
In a preferred embodiment the installation includes a device for recovering the oxygen present in the exhaust gas, which comprises means for the centrifugal separation of the carbon dioxide utilizing the different inertias and viscosities of the two gases.
In a preferred embodiment the installation includes a device for removing the combustion products from the circuit of the internal combustion engine and for recovering the residual oxygen, which comprises a low pressure enclosed compressor, means for the automatic monitoring of the gas delivery rate of the compressor with a sensor to detect variations in the gas pressure in the circuit, a water pump system and treatment tank(s) for gas-sea water treatment with minimum energy consumption constant at all immersion depths, and with automatic monitoring of the weights of the treated media.
Means to separate the water by condensation and store the separated water on board may be provided in the device for removing the combustion products in manner known per se.
In a preferred embodiment, the compressor belonging to the device to remove the combustion products is provided according to the invention with a throttle flap arranged in the intake pipe, which permits a regulation of the delivery rate of the compressor in the sense that the pressure in the circuit of the internal combustion engine exhibits a constant value.
To control the throttle flap, a pneumatic and/or electric-electronic control device influenced by the absolute pressure in the circuit is preferably provided.